With the introduction of Nazjatar in 8.2 pet battlers were not left out. There are in total 12 legendary pets lurking in the depths waiting for unwary pet battlers.

This time there is no family achievement to be done for the new fights. Instead we got a task that is a lot easier than most of the previous achievements. Beating every pet battle boss in Nazjatar grants Nautical Nuisances of Nazjatar which on its own doesn't give you anything.
However it is one of the 4 requirements to Team Aquashock; a meta achievement that rewards you with the awesome pet Kelpfin! To get this you'll have to beat all the legendary pets and capture every wild pet in both Mechagon and Nazjatar.

Even though there are quite a lot of fights scattered across the area it doesn't take much to defeat them.
The zone is pretty large and hard to navigate through, making it difficult to find every single boss but if you are using TomTom you can copy those coordinates to locate them.

"The daily legendary quests on Mechagon and Nazjatar can be done with a Voodoo Figurine, Infected Squirrel, and a 3rd undead pet that has abilities that’re strong against the legendary you’d be facing."

This immediately hit me in the rose-tinteds, because this was a combo I loved back in Mists.

There are a couple of variations.

Sen'jin Fetish can usually replace the Voodoo Figurine, and I prefer it in this combo, because it has more Health and more Power, and as an Undead against Legendaries, the Figurine's slightly higher Speed doesn't usually help. I will therefore refer to the Fetish hereafter.Infected Squirrel is usually the better of the two undead squirrels for this, because of Corpse Explosion, but Blighted Squirrel with Woodchipper and Stampede is the winner when its Crouch is needed to guarantee surviving long enough. My preferred breed for both is H/P.

The general method is this:

Sen'jin Fetish:

1. Flame Breath until you have one round left to live. This is not always easy to predict, but ideally, you want to keep repeating Flame Breath until you can get off just one Wild Magic before you are brought to zero. The sequence will obviously depend on the damage the target does. If you're really stuck, just keep alternating Flame Breath and Wild Magic.2. On your Undead round, use Rot. This makes the target take damage as Undead for 5 rounds.

Infected Squirrel:

1. Apply Creeping Fungus2. Stampede until your Undead round, or if you will live only one more round before becoming Undead, and Stampede is over, Corpse Explosion. The idea is to stack Corpse Explosion as your last act, and/or to leave the target with two rounds of Shattered Defenses.

So I just went around Naz and Mech and knocked down 7 of them with this combo. It's great to use it again! I haven't had to use my third pet yet. Probably something will require the third pet.

This general method doesn't constitute a detailed strat, but I commend it as an interesting base to anyone who is looking for alternatives.

sure does ... it would be helpful also if they were placed in the notes of each battle as well, but since most people don't put it there, it is wonderful having it all in one place :-) a lot less work than searching for each one for sure.

I had a big issue with Kelpstone being phased out when I arrived to do the battle! I wrote to blizz to ask what was going on. Here is their response. (Thank you blizzard for getting back to me so quickly allowing me to get my achievement done!)

"It looks like Kelpstone can be phased out if you're on the quest "What Will It Lure" which it looks like you're currently on. If you finish that up, you should be in the right phase."

Side note, don't abandon the quest, it does not work, it's a simple quest and takes all of five minutes to complete, best to get it out of the way.

Can't you just look at the achievement in your Achievements panel in-game and see which ones are ticked? It's not like the Family achievements, where you have to defeat each numerous times, so it should be easier to follow.